I’ll admit that many of these portals are level dependant or rely on quest chains being completed, but to the savvy (or lazy?) level 85 most if not all options should be available or can be had quickly if they’re not. I apologise in advance for the slight Alliance bias but I don’t yet have a level 85 Horde. /hangs head in shame.

Stormwind/Orgrimmar

Firstly from Stormwind and Orgrimmar there are portals to all the Cataclysm zones including Tol Barad all have to be opened by questing and means that they are level dependant. Most of these zones have a portal back to Stormwind /Orgrimmar too which is cool and maybe sometime soon we’ll end up with an Uldum portal although Vash’jir would be troublesome because of the way the portal phases you into your current phase questing base.

From all major cities there are portals to the Blasted Lands that port you real close to the Dark Portal which allows fast access to Outland. These are located near the mage trainers in each city:

Now from the Hellfire Peninsula side there is now a portal back to Stormwind /Orgrimmar, I don’t know when this got added but the 2 things I know are that it wasn’t a working portal in TBC but it IS now!:

This one is boosted in effectiveness because if your faction control Wintergrasp, you can port there from Dalaran and then fly manually the short distance to the waygate inSholazar Basin. There is also a convenient return to Dalaran from Wintergrasp meaning you can use this as a shortcut back to Dalaran too:

There are other tricks too. If you stuck in Darnassus and want to get back to Stormwind you could use the boat but if the Darkmoon Faire is in town speak to one of their representatives who will port you to Goldshire or just outside Thunder Bluff for a small, level dependant fee. Along with a host of other trinkets, tabard’s and doodads to fling you around the world of Azeroth but the ones here are all free or very cheap to use.